except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to
... etary rights. Cover illustration: The title image is a collage of three different Arabidopsis thaliana plants. The endogenous activity of one of the major cell cycle kinases cyclin-dependent kinase A;1 (CDKA;1) increases from left to right. The two left individuals are cdka;1 homozygous null mutants that were partially complemented by phosphorylation-site substituted CDKA;1 variants and are compared to a wild type plant of the accession Columbia-0 on the right. The phosphosite mutants were expressed from the endogenous CDKA;1 promotor. The CDKA;1 variant on the left carries the double phospho-mimetic substitution T14D/Y15E in the ATP-binding pocket (P-loop) and that one in the center the single amino acid substitution T161D in the activation loop (T-loop). Both domains of CDKA;1 are required for catalysis and substitutions lead to a tremendous reduction in kinase activity. For reference, see Dissmeyer N.